The therapeutic use of some analgesic compounds are often limited because of potentially adverse and dangerous side-effects. However, combinations of analgesics with different mechanisms of action could enhance analgesic efficacy (synergy) while reducing the dose-dependent adverse effects of the individual components. The development of combination analgesics that are synergistic, therefore, would effectively reduce the dose of each compound, thus reducing the adverse effects while maintaining analgesic potency. Combinations of acetaminophen with opioids (i.e., hydrocodone, codeine) are frequently prescribed for acute and chronic pain management. However, although acetaminophen combinations have greater efficacy for moderate to severe pain and are some of the most popular prescription analgesics on the market, it has been recognized that even at therapeutic doses acetaminophen (andcombinations containing acetaminophen) can cause liver toxicity. Thus, a drug with a similar analgesic profile to acetaminophen, but with little or no hepatotoxicity, would be a valuable substitute for acetaminophen in these combinations. Phase I supported the development of a non-toxic acetaminophen analog (SCP-1) in which we explored the feasibility of using this compound in combination with other opioid and nonopioid analgesics. Our goal was to identify two SCP- 1 combinations (one opioid and one nonopioid) that displayed synergistic analgesic properties, and would be the basis for further drug development in Phase II. Based on their superior synergistic analgesic profile, SCP- 1+codeine and SCP-1+clonidine combinations were identified as candidates for further development. Under Phase II support we will evaluate and screen further the analgesic profiles and adverse side-effects of different SCP-1 : codeine and SCP-1 : clonidine combination ratios (i.e.formulations). These results will be the basis for conducting key early stage pre-clinical GLP safety studies under Phase II that will be used in our IND applications to the FDA.In Phase III we will conduct Phase I human clinical trials to evaluate tolerability and oral bioavailability in normal human volunteers, and Phase II human clinical trials to evaluate the combinations in postoperative pain patients.